A study found that the Covid vaccine prevented one in 10 infections six months after its administration.
New Zealand researchers reached their conclusions after evaluating data on more than 5 million people since December 2020, when the country’s first jabs were rolled out in February last year.
Of these, 4 million were vaccinated and nearly 1 million never received the Covid vaccine, and vaccinated individuals were matched by age and sex to their unvaccinated counterparts.
The scientists then used patient data to assess the effectiveness of the shots against various Covid outcomes, including infections, hospitalizations and deaths.
Publish your results New Zealand Medical JournalResearchers evaluated outcomes based on receipt of a second Covid booster.
New Zealand researchers reached their conclusions after evaluating data on more than 5 million people since December 2020, when the country’s first jabs were rolled out in February last year.
Although ZAB has been shown to provide long-lasting protection against viral death, protection against infection is dramatically reduced.
It was found to stop infections by 57 percent in the first month people received the vaccine. But six months later that dropped to just 9.9 percent.
JAB-based protection against Covid hospitalisation was good, although significant declines were also recorded.
Vaccinated people enjoyed 82 percent protection against hospitalization in the first month after contracting the virus. But within six months, that had dropped to just 49 percent.
The authors note that it was not possible to carry out a comparative analysis of these results with those who received a second booster, since there were no deaths from Covid in the vaccinated group.
This is not the first study to show that the efficacy of the Covid vaccine decreases over time.
Exact numbers depend on the stage of the global pandemic, the variant circulating at the time, and may also vary by brand.
A 2021 US study found that Covid shots used in the US had dropped from 85 per cent effective against infection to about 50 per cent at six months.
A Qatari study, also from 2021, found that even Pfizer’s Covid vaccine was only 20 percent effective at preventing people from becoming infected after six months.
Covid vaccines, which ended the crippling lockdown, lost their protective power due to two factors.
For one, the body’s initial surge of antibodies designed to attack the Covid virus fades over time, though experts say some long-term protection persists.
Secondly, the virus itself evolves over time, with new variants evolving with slight differences, meaning they are better able to evade the protective punches offered by older strains of Covid, which they were designed to combat.
That’s why updated shots, designed to target the new ones, are now circulating more widely, and strains of the virus are being used in later Covid booster campaigns.
The vaccine was found to stop 57 per cent of infections among Kiwis in the first month. But six months later this had dropped to just 9.9 per cent.
The phenomenon of waning immunity is not unique to Covid either, which is why some people, such as the elderly and health care workers, receive a new flu vaccine each year designed to target new versions of the circulating virus.
It is also worth noting that the same basic problem occurs with natural immunity to Covid infection – this protection diminishes over time.
The authors say that while their study is strengthened by its large number of participants and reliable crowdsourced data, it has several limitations.
One is that the reduced number of unvaccinated people may have influenced the results, making it more likely that the vaccine’s efficacy was underestimated.
Another is that they targeted people who couldn’t trace specific brands of the Covid vaccine, meaning this metric couldn’t measure any difference.
Furthermore, the authors stated that for most of the study period, it was not possible to distinguish between different Covid variants due to the predominance of omicron variants.
They said future studies were warranted, tracking the effectiveness of the shots over six months and differences in outcomes by vaccine type and Covid variant.
